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Sulfur nanoparticles were obtained in an aqueous solution of L-cysteine, sodium citrate, and sodium sulfide by using a hydrothermal method of synthesis. The luminescent optical properties of the nanoparticles were investigated using absorption spectroscopy and photoluminescence. Influence of the composition of the system components on the luminescent properties of nanoparticles was investigated. A series of syntheses was carried out changing the volume fractions of L-cysteine (Series 1) and sodium sulfide (Series 2) from 1 to 10 ml. It was noted that with an increase of L-cysteine content changes pH value from 7 to 5 and the presence of absorption maxima only in the range of 200-300 nm. Instead, an increase in the amount of sodium sulfide is accompanied by a change in the pH value from 7 to 12, and, the appearance of absorption maxima in the long-wavelength region. The presence of absorption maxima in the range of wavelengths from 200 to 700 nm in solutions of both series is likely due to the formation of polysulfide ions up to S4 2- in the Series 1 and up to S8 2- in the Series 2 and to their subsequent oxidation into sulfur nanoparticles. The resulting colloidal systems with sulfur nanoparticles are stable over time and have photoluminescent properties, which makes them promising for further application in various fields, in particular, chemistry, medicine, and materials science.
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